The present invention relates generally to the art of conveying materials, such as soil, stones and like granular solids from an excavation site for delivery to a remote location. More particularly, the present invention relates to a method and apparatus for conveying such granular solids from holes, trenches and like excavation sites, which employs a very strong vacuum generated by a high velocity stream of a gas, preferably flowing in the supersonic regime. The present invention is particularly suited, though not exclusively, for use in connection with excavation work being carried out in close proximity to utility lines, conduit, pipe and the like, where conventional mechanical equipment may cause damage to such service lines and, in the case of natural gas pipe, can even create explosion hazards.
Heretofore, when excavation has been required in close proximity to fragile utility lines, it has been necessary to convert from the usual mechanized equipment, such as power shovels, backhoes or the like and employ hand excavation tools such as picks and shovels to complete the task. Hand excavation not only results in a dramatic reduction in the material removal rate, but it also does not completely solve the problem of inadvertent striking and damaging of buried utility lines and pipes.
The problem of loosening soil in such excavation work has been solved by the invention disclosed in co-pending patent invention entitled: "Method and Apparatus for Excavating Soil and the Like Using a Supersonic Gas", U.S. Ser. No. 877,280, filed June 23, 1986 and assigned to the assignee of the present application. The invention disclosed therein is directed to a method and apparatus which employs a nozzle supplied with high pressure gas, preferably air, to generate a supersonic jet which creates fissures and cavities in a soil mass. The impacting, high velocity air stream becomes stagnated within the soil cavities, causing rapid fracture of the local sites resulting from the rapid release of expanding high pressure air trapped within the soil cavities and fissures. The stagnated air mass must expand and, in so doing, causes the soil to violently fail in tension. In order to remove loosened soil from an excavation site, it has heretofore been common practice to employ a conventional hand shovel, which once again results in a time consuming manual labor operation. The present invention is particularly suited for use as a replacement for the manual shovel work for the removal of the loosened soil from an excavation site, and is particularly useful, in combination with the invention disclosed in the abovereferenced commonly assigned co-pending application.
The present invention is directed to a method and apparatus for withdrawing and conveying loosened soil, stones and like solids from an excavation site. The invention employs a jet of gas, preferably air, moving at supersonic velocities to create a high vacuum at an inlet end of the device and to provide a fast, efficient and safe technique for material removal in this heretofore labor-intensive and tedious task. The invention is suitable for use in many forms, such as a hand held tool, or it may be frame mounted on a mobile excavation machine, or it may be used in conjuction with a fully automated machine, such as, a robotic excavator apparatus, to name only a few of such potential applications.
The invention provides a device and method for safely excavating soil in close proximity to natural gas lines, water pipes, sewer lines, underground power cables, telephone lines and the like, which is extremely aggressive in soil removal while being completely harmless toward the buried objects, including those of a very fragile nature. The invention further provides significantly higher productivity than conventional hand methods, with virtually no likelihood of accidental destruction of subterranean objects. The high vacuum present at the inlet region of the device causes an evacuation of solid material from difficult to reach areas such as beneath or behind pipes, where shovels can not fit or are awkward to maneuver.
The invention in a preferred form utilizes a supersonic gas jet, the air supply for which is conveniently generated by a conventional air compressor unit of the same type which supplies compressed air to the supersonic jet excavation device of the co-pending patent application referred to above. The present invention provides a solids conveyance device which is simple to operate, safe to use and which is operable in conjunction with conventional, commercial air compressors. Still further, the invention is suitable for use in conveying a wide range of soils, from very dry and brittle types, to moist sands, loam and other gummy-type soils, while also being capable of conveying stones and rocks mixed therewith. The vacuum tube portion of the device is preferably constructed of lightweight materials, such as plastic or aluminum, thus making the apparatus less burdensome to operate while also rendering it non-sparking in explosive environments.
A hand-operated embodiment of the present invention incorporates a pneumatically efficient valve mechanism which employs the compressor reservoir gas at high pressure to open the valve against the same high pressure supply. The present invention further provides a high velocity vacuum solids conveyance device in which the gas injector nozzles are located outside of the flow path of the vacuum tube so as to minimize abrasive wear to the injector nozzles while, at the same time, increasing the throughput and efficiency of the device by providing an unobstructed constant cross-sectional flow path. The injector nozzles are aligned at a low angle of incidence relative to an axial centerline of the vacuum tube providing minimum abrasive wear to the bore sidewall surface as well as preventing an excessive formation of solids build-up within the bore at the section where the jets intersect. The invention further includes a mixing tube section downstream from the injector nozzles to provide for an adequate momentum exchange to produce a sensibly homogeneous suspension of solids moving under sensibly steady conditions. At a downstream, discharge end of the mixing tube, is a diffuser section which causes a deceleration of the gas stream in a relatively short distance, thereby providing a means of reducing the losses associated with the kinetic energy of the gas.